In electrostatic copying, an electrostatic latent image is formed on an element. That image can be developed into a visible image by the application of toner powder thereover. The resulting toned image is then transferred from the element to a receiver to which the transferred toned image is fixed, usually by heat fusion. The transfer of the toned image to the receiver has usually heretofore been accomplished electrostatically, using an electrostatic bias applied between the receiver and the element.
In order to produce copies of very high resolution, it is necessary to use toner particles that have a very small particle size, that is, less than about 8 microns.
Electrostatic transfer of such very small toner particles, particularly of those having a particle size less than about 6 microns, is difficult to accomplish because, the forces of adhesion holding the particles to the photoconductor are greater than the electrostatic transfer forces that can be applied. Moreover, Coulombic repulsion between the particles tends to scatter such particles causing loss in transferred image resolution and increase in grain and mottle. To avoid these problems an improved electrostatic transfer process must be used with toned images of such particles.
However, so far as now known, no electrostatic transfer process is known by which a high resolution toner powder image comprised of very small toner particles can be transferred from an element to a receiver that is treated at the time of copying with a preliminary coating produced from toner particles.